Long-term sediment yields from glacierized basins on Mount Baker, 1947-2015

Abstract

Where glacierized watersheds are adjacent to population centers, sediment-laden rivers may catastrophically flood and the frequency of such flooding has been predicted to increase along with increased sediment supply. Despite these concerns, upland sources of sediment and sediment connectivity between proglacial uplands and downstream river plains are poorly understood. We utilize automated Structure from Motion software to process historical aerial imagery and, in tandem with publicly available LIDAR data, produce a DEM time series with coverage that spans from 1947 to 2015 in glacierized watersheds on Mount Baker, a stratovolcano in Washington State. We measure basin-wide sediment yields in 10 distinct basins and quantify the relative sediment contributions of different upland erosion processes. Sediment yields are correlated with lithology, Little Ice Age moraine slope, upslope contributing area, and glacier retreat. We found that upslope contributing area and moraine slope are the strongest predictors of basin-wide sediment yield, and stream channel slope is a poor predictor of sediment yield, indicating that debris flows originating from glacier moraines are a primary erosion mechanism in proglacial basins. Our estimates of proglacial sediment yields account for 10 to 56% of estimated total sediment load in the Nooksack river, which drains multiple basins on Mount Baker, and sediment input from proglacial basins exceed contributions from erosion of glacial and volcanic terraces. On intra-decadal timescales, the irregularity of hillslope erosion events disconnect proglacial sediments from the downstream system. On decadal timescales, infrequent debris flows bypass proglacial stream channels and carry sediment downstream of proglacial limits. Our findings indicate that pro-glacial sediments may contribute a significant portion of riverine sediments where upland topography and lithology are favorable and when the climate is relatively wet.